1. Field of Invention
This invention relates generally to pneumatic tires and more specifically to asymmetrical, directional tires.
2. Description of Related Art
In automotive vehicles, proper traction between the tire and the road surface is necessary for effective operation of the vehicle. Tires are required to provide good traction under a variety of different operating conditions. For example, when the vehicle accelerates, the tire must transfer the force to the road surface with a minimum of slippage to achieve maximum acceleration. Similarly, when the vehicle is decelerating or braking, the tire must transmit this force to the road with a minimum of slippage to maintain controlled operation of the vehicle. When cornering, the tire is required to maintain good contact with the road surface despite the weight of the vehicle shifting on its chassis and the presence of cornering forces. The presence of rain, snow or other friction-reducing substance on the road surface makes all of the above traction objectives more difficult to achieve.
Tire designers have sought to design tread patterns to improve traction between the tire and the road surface. Some have been specifically directed toward good traction under a variety of road surface conditions such as U.S. Pat. No. 4,545,415 to Lindner et al. and U.S. Pat. No. 3,674,077 to Verdier. Both Lindner et al. and Verdier disclose tire tread designs featuring grooves which extend generally laterally across the tire tread from tread edge to tread edge. Other tread designs feature directional treads which are designed to rotate in one direction only, such as U.S. Pat. No. Des. 284,178 to Kawabata et al. and Austrian Patent No. 147,223. Still other tread designs seek traction advantages through asymmetric tread designs such as U.S. Pat. No. Des. 223,599 to Busch et al.
While tire tread designers have met with some success, further improvements are desirable in providing good traction under a variety of operating and road surface conditions.